Control system



April 15, 1924. 1,490,216

' H. L. KEITH CONTROL SYSTEM Filed May 23, 1919 00411) onfocfor INVENTOR W'TNESSES' 4 Haro/dL/fe/f/v.

Patented Apr. 15, 1924.

UNITED STATES PATENT OFFICE.

HAROLD L. KEITH, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HO'USE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

CONTROL SYSTEM.

Application filed May 23, 1919. Serial No. 299,182.

To all whom it may concern:

Be it known that I, HAROLD L. KEITH, a citizen of the United States, and a resident of Vilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Control Systems, of which the following is a specification.

My invention relates to motor-control systems and particularly to systems for controlling compound-wound direct-current motors during the period immediately following their starting operation.

The object of my invention is to provide an improved control system of the above designated character.

My invention relates more particularly to control systems for compound-wound motors involving the use of a line contactor for connecting the motor to a source of energy and having an energizing coil that is controlled by a relay which, in turn, is adapted to be closed by a coil that is in circuit with the shunt field-magnet winding. Owing to the transformer action which takes place between the series and shunt fiel.dmagnet windings immediately following the operation of closing the above-referred-to line contactor, the relay coil becomes ineffective to maintain the relay closed, so that the contactor coil becomes temporarily ole-energized, with the result that the contactor becomes opened by gravity and the motor stops.

7 In a co-pendin application by E. M. Benton and G. W. Hurtt, Serial No. 302,702, filed June 9, 1919, and assigned to the Westinghouse Electric & Manufacturing Co, this difliculty is avoided by the use of an additional relay for controlling the line-contactor coil that is itself controlled by a coil that is energized in accordance with the voltage of the accelerating resistor. According to a modification, the second relay is dispensed with and its coil is employed for controlling the same field relay.

According to my invention, the desired result is effected without the use of additional relays or additional coils, but by the simple addition of a small resistor.

In the accompanying drawing, the single figure of which is a diagrammatic view of a system arranged according to my invention. the armature of the motor is shown at 1, the series field-magnet winding at 2 and the shunt field-magnet winding at 3. The shunt field-magnet winding 3 is normally connected to line conductors 4 and 5 in circuit with the actuating coil 6 of a field relay 7. The armature 1 and the series field-magnet winding 2 are adapted to be connected in series with an accelerating resistor 8 to the line conductors 4 and 5 by a line contactor 9 having an actuatin coil 10, the circuit of which is controlled both by the field relay 7 and a master switch 11. The accelerating resistor 8 may be short-circuited in any well-known manner, the method shown in the drawing for purposes of illustration involving the use of a lookout contactor 12 and a contactor 13 having an actuating coil 14 that is controlled in accordance with the counter-electromotive force of the motor.

A resistor 15 is connected, at one end, to that side of the coil 10' which isnot connected to the line conductor 5' and, at the other, to an intermediate point 16 of the resistor 8. By means of this connection, as described hereinafter, the coil 10-is adapted to be subjected to the voltage drop of so much of the resistor as is between the points indicated by the reference numerals 16 and 17. The junction point 16 may be any point of the resistor other than the point 17 and may, indeed, be the other terminal, indicated at 18, of the resistor 8.

As the field-magnet winding 3 is nor- 7 mally connected to the line conductors 4 and 5, current normally flows through this fieldmagnet winding 3 and through the relay coil 6. The relay 7, therefore, is normally maintained in closed position, as illustrated. To start the motor, the master'switch 11 is closed to establish a circuit from the line conductor 4, through the relay 7, the coil 10 and the master switch 11, to the line conductor 5. The line contactor 9 becomes thereupon closed by its actuating coil 10to establish the armature circuit from the line conductor 4:, through the series field-magnet winding 2, the armature 1, the line contactor 9, the actuating coil of the lookout contactor 12 and the resistor 8 to the line conductor 5.

Immediately upon the energization of the above-traced armature circuit, the field-magnet windings 2 and 3 become subjected to a transformer action which has the effect of reversing the current traversing the field magnet winding 3 and the coil 6. The relay 7, consequently, drops open by gravity. The opening of this relay 7, of course, results in the opening of the circuit of the coil 10. The energization of the armature circuit, however, results also in subjecting the coil 10 to the voltage drop of so much of the resistor as is contained between the points 17 and 16, for the coil 10 is connected in a parallel circuit to the resistor which extends from the junction point 17, through the master switch 11, the coil 10 and the resistor 15, to the junction point 16. The line contactor 9 is consequently maintained closed by its actuating coil 10 during such period as the transformer action of the field-magnet windings 2 and 3 takes place, irrespective of the position of the field relay 7. This transformer action lasts for but a very brief period of time so that, by the time that the contactors 12 and 13 have become closed, in a well-known manner, to ellect the short-circuiting of the resistor 8 and the consequent de-energization of the above-traced parallel circuit for the coil 10, normal conditions have again become established, current again flows through the coil 6 in its normal direction, and the field relay 7 has again become closed to maintain the normal circuit of the coil 10 closed. The motor, therefore, continues to operate, the line contactor 9 being maintained in closed position by the field relay 7.

It will be noted that, according to my invention, additional relays or coils are unnecessary, the only additional apparatus required being the small resistor 15.

I claim as my invent-ion:

l. The combination with an electric motor having an armature and field-magnet windings in series therewith and in shunt thereto, a resistor in series with said armature, a switch for closing the circuit of said motor having an actuating coil, and a switch for controlling the circuit of said coil having an actuating coil in circuit with said shunt fieldmagnet winding, of means for connecting the first-named coil. across a portion of said resister.

2. The combination with an electric motor having an armature and field-magnet windings in series therewith and in shunt thereto, a resistor in series with said armature, a switch for closing the circuit of said motor having an actuating coil, and a switch for controlling the circuit of said coil having an actuating coil in circuit with said shunt ficldmagnet winding, of means for sub1ecting the first-named coil to the voltage of said. resistor durin the period of transformer action of said held-magnet windings.

3. The combination with an electric motor having an armature and field-magnet windings in series therewith and in shunt thereto, a resistor in series with said armature, a switch for closing the circuit of said motor having an actuating coil, and a switch for controlling the circuit of said coil having an actuating coil in circuit with said shunt field-magnet winding, of a resistor connected in circuit with the first-named coil across said armature resistor.

a. The combination with a dynamo-electric machine having a field winding, astarting device therefor, a switching device for controlling said machine and having an actuating coil, and a switch for governing said switching device and having a coil controlled by said field winding, of means for connecting the first-named coil across a poition of said starting device.

5. The combination with a dynamo-electric machine having a series and a shunt field winding, a resistor in circuit with said machine, a switching device for controlling said machine and having an actuating coil, and a switch for governing said device and having a coil controlled by the current in said shunt field winding, of means for energizing the first-named coil in accordance with the voltage of said resistor during the. period of transformer action of said windings.

6. The combination with an electric motor having a shunt field-magnet winding, a. main resistor in series relation with said motor, a switching device for closing the circuit of said motor and having an actuating coil, and a switch having contact members for con trolling the circuit of said coil and having an actuating coil in circuit with said fieldmagnet winding, of a resistor connected between a predetermined point of said main resistor and a point intermediate the coil of said switching device and said contact members.

7 The combination with a motor having a shunt field winding, of a line switch having an actuating coil, a relay controlled by the shunt-field-winding current for controlling said coil, said coil bein controlled independently of said relay t uring acceleration of the motor.

8. The combination with a motor having a shunt field winding, of a line switch having an actuating coil, a relay cont-rolled by the shunt-field-winding curient for controlling said coil, said coil being controlled in accordance with the motor-armature current independently of said relay during the accelerating period.

In testimony whereof, I have hereunto subscribed my name this 16th day of May,

HAROLD L. KEITH. 

